Emile Baudot dedicated his life to the development of a fast-printing telegraph. After successively improved versions, he demonstrated at the International Exhibition of Electronics a perfected model which could transmit six simultaneous messages. The Baudot system was used throughout the world for terrestrial and undersea telegraph links for over 70 years.
Jean-Maurice-Emile Baudot was born in Magneux (Haute-Marne) the 11th of September, 1845. He was the son of a farmer. After receiving only a primary education, he spent his adolescence in agricultural work on his father’s farm. Until his admission, as an alternate, to the Administration of Telegraph Lines (July 16, 1870), he lived a rural life, in an environment that in no way seemed to predestine him to become the genial inventor that he later was.
It was only after his entry into the Administration that, seduced by the scientific side of his new profession, he enterprised to perfect his general education: he had everything to learn, in electricity and in mechanics! He put himself resolutely to this task, and in the short instants of leisure that his professional occupations left him, at the Central Post in Paris, he put his forehead, with a marvelous power of work, to the research that came to him from his enterprise on telegraphic apparatus and the study of science, without which the first would have been sterile.
Promoted to Controller in 1880, after the first sucess of his system, he had the ambition to become an Engineer: without neglecting for this the work again in infancy, and without being frightened of the difficulties that it gave him to surmount, he prepared for the test, took it with success, and was named Inspector-Engineer in 1882.
Being an engineer at the French Telecommunications Service, Emile Baudot was working on a way to improve the efficiency of the then very slow telegraphic transmission. He had to overcome many difficulties, especially the avoidance of timing errors between phases of transmission and reception. Finally he developed what is called “the Baudot printing telegraph”. Today it would be called a synchronous time division multiplex system. Baudot invented his telegraph code in 1870.
By 1874 or 1875 (various sources give both dates) he had also perfected the electro-mechanical hardware to send his code. Actually, his inventions were based on certain printing details from the Hughes instrument, a distributor invented by Bernard Meyer in 1871, and the five unit code devised by Gauss and Weber. Baudot combined these, together with original ideas of his own, to produce the final multiplex system.
The Baudot code is the first truly digital one. It consists of only two states, both logically and electrically. Logically, the only states are “1″ and “0″. Today we call the unit that can have these two logical states a “bit”. Electrically, the states are current flowing (or “1″), and no current flowing (or “0″). Each character consists of 5 bits. Two logical states and five bits allows 32 characters.
Baudot needed 26 characters for the alphabet, 10 for numbers, and more for miscellaneous characters. In order to increase the number of characters, he used two special characters, LTRS and FIGS, to give a total of 64 possibilities. LTRS (11111) precedes Alphabetic characters. FIGS (11011) precedes numerical and special characters such as punctuation. In 1874 he received a patent on a telegraph code that by the mid-20th century had supplanted Morse code as the most commonly used telegraphic alphabet. The Baudot code came to be known as the International Telegraph Code No. 1.
Here is a chart that shows all the possible Baudot combinations.
This diagram depicts a five-unit Baudot code. The characters depicted are the letters “W”, “K”, and “D”. The “W” (the top character) is sent or received first A hole in the appropriate bit position indicates a Mark (logic 1). The lack of a punched hole indicates a Space (logic 0). The smaller holes in the middle of the tape fit over a sprocket which feeds the tape through the tape punch or reader.
One more example of paper tape with 5-bit Baudot code
The hardware had three main parts. They were the keyboard, the distributor, and a tape. On June 17, 1874, Baudot patented, under the number 103,898 and the title “System of rapid telegraphy” his first apparatus, which was both multiple and really printing, since the conventional signals were translated automatically into typographic characters.
The keyboard, seen at the left, had five piano like keys. A spacer separated the keys into one group of two and another of three. The operator entered the five bit code for each character at the keyboard. The keyboard input went to the distributor. Once the keys have been pressed they are locked down until the brushes have passed over the segments connected to that keyboard.
Remember that there may be four or more keyboards connected to one distributor. The keyboard is then unlocked ready for the next character with an audible click to warn the operator, known as the cadence signal. Working the Baudot keyboard required a lot of skill. The operator had to keep up a steady unvarying, rhythmic pace. The usual speed of operation being 180 letters per minute.
The type keys worked by two fingers of the left hand and three fingers of the right hand. The five unit code employed by the system was arranged to be easy to remember.
The Baudot distributor, pictured on the left, was the central to the operation of the system. Both the transmitter and the receiver used a distributor. On the transmitter end, a keyboard was connected to a set of metal brushes inside the distributor.
The brushes, rotated by either weights or an electric motor, made and broke contact with stationary conductive elements called segments. Typically, each system had four to six keyboards, each connected to its own set of brushes and segments in the distributor. Each set connected to a single communications line. This was the first successful multiplexing system in electrical telecommunications. Correcting currents were sent down the line to keep the brushes in synch at the two ends.
Two other kinds of the Baudot’s distributor, ca. 1880
The receiver is also connected to the distributor. The signals from line are stored on a set of five electromagnets. The combination is then decoded to print the character on paper tape.
Because of the high signal attenuation inherent in wire, transmission over distances greater than a few kilometres requires the use of regularly spaced repeaters to amplify, restore, and retransmit the signal. The picture shows repeater and relay units used in early Baudot-type telegraph.
The Baudot system was accepted by the French administration in 1875. The first on-line tests of his system took place between Paris and Bordeaux on November 12, 1877. At the end of 1877, the Paris-Rome line (about 1700 km) began to be served by a double Baudot telegraph system. The first telegrams transmitted were those announcing the election of Mr. Carnot to the presidency of the French Republic.
In July, 1887, he undertook tests crowned with success between Weston and Waterville on the cable of the “Commercial” Company; the apparatus experimented with was a double Baudot installed in duplex. The Baudot transmitters and receivers were substituted purely and simply for the recorder.
On August 8, 1890, he assured, on a single wire, discrete relations between the three towns of Paris, Vannes, and Lorient, inaugurating at this date the spread-out posts that were later so much generalized. On April 27, 1894, he established, always over a single wire, communications between the Paris stock exchange and the Milan stock exchange, and at the same time between the central Paris and central Milan, and invented for this occasion the retransmitter. On January 3, 1894, he served with a triple apparatus the underground wires from Paris to Bordeaux that functioned painfully with the Hughes telegraph system.
The Baudot apparatus installed at the Universal Exhibition of 1878 won him the great gold medal and the unanimous congratulations of the engineers of the entire world. The Baudot telegraph system was employed progressively in France, and then in other countries; Italy was the first to introduce it, in 1887, in its interior service; Holland, in 1895; Switzerland in 1896, Austria and Brasil in 1897, England in 1898, Germany in 1900, Russia in 1904, the British Indies in 1905, Spain in 1906, Belgium in 1909, the Republic of Argentina in 1912, and Romania in 1913. The British Post Office adopted it for a simplex circuit between London and Paris in 1897. The inventor obtained the knight’s cross from the Legion of Honor in 1879, and was made an officer in 1898.
In these times, Mr. Baudot solved with his apparatus the most varied and the most interesting problems. However, Baudot has little help from the French Telegraph Administration to improve his system. Very often he had to find the financial source for his research in his own pocket. For example, in 1880 he sold his great gold medal received on the International Exhibition of Paris in 1878 to perform further research on the telegraphy.
Baudot died on March 28, 1903, at Sceaux, France, near Paris, at the age of fifty-seven, after a long time illness.
A unit for the speed of telegraph transmission, Baud, was named after Baudot (Baud is short for Baudot). Baud was the prevalent measure for data transmission speed until replaced by a more accurate term, bps (bits per second). One baud is one electronic state change per second. Since a single state change can involve more than a single bit of data, the bps unit of measurement has replaced it as a better expression of data transmission speed. In English, 45.5 baud is about 60 words per minute (wpm).
French post office released a special stamp devoted to Emile Baudot in 1949 on the occasion of the International Congress of Telegraph and Telephone. However, this stamp has been printed with an error – Baudot was born in 1845, but not in 1848 as it was claimed on the stamp. The stamp has been corrected and printed again with a different color. However, the erroneous stamps still circulate among the philatelists and they have higher value than the corrected stamps.
A telephone card with a portrait of Emile Baudot and with a picture of his telegraph unit memorizes the French inventor.